For lithographic fine patterning in semiconductor manufacturing processes, there has been a demand for resist compositions that can be exposed at shorter wavelengths and show a wide depth of focus tolerance (abbreviated as “DOF”), a small line edge roughness (abbreviated as “LED”), high resolution, high sensitivity, good substrate adhesion and good etching resistance.
It is reported that the introduction of a fluorine atom or an aliphatic moiety into a resist resin would produce a certain effect on the reduction of the exposure wavelength. The use of a fluorine-containing sulfonic acid of high acidity as an anion moiety of an acid generator is being attempted in order for a resist composition to attain a wide depth of focus tolerance and a small pattern line edge roughness. The formation a resist resin with an acid generator function is also being attempted for improvements in resist characteristics. These types of resist resins have been proposed, each containing a sulfonic acid onium salt as an acid generator in a side chain of the resin with an anion moiety of the acid generator fixed to the resin (see Patent Documents 1 to 7). For example, Patent Documents 6 and 7 disclose resist compositions using resins each obtained by polymerization or copolymerization of a methacrylic acid ester containing in a side chain thereof a triphenylsulfonium salt of sulfonic acid having a fluorine atom at its α-position.
However, the sulfonic acid onium salt-containing resins have significantly low solubility in ordinary resist solvents (such as propylene glycol monomethylether acetate). There thus remain various problems, e.g. that it is difficult to incorporate a large amount of sulfonic acid onium salt structure in the resist resin and that the kind of a monomer copolymerizable into the resist resin is considerably limited.